In this work, we present an Observer-based Economic Model Predictive Control (OEMPC) scheme for Direct Contact Membrane Distillation (DCMD). To compute control actions via MPC strategy, full knowledge of the system states is necessary to predict the future evolution of the system. However, the full state measurement for DMCD is either difficult or costly. In this work, an integrated framework of an observer design and EMPC paradigm is proposed for the DMCD process. Numerical simulations are presented to illustrate the performance of the proposed observer design. Closed-loop simulations show that the proposed OEMPC scheme was able to operate the process economically while satisfying process and input constraints.